1. The Field of the Art
The present invention relates to taps for connecting a device to a coaxial cable transmission line so that carrier signals of varying frequencies and DC power can be efficiently transmitted to and from the device attached to the coaxial cable transmission line.
2. Description of the Prior Art
When transmitting RF signals along a coaxial cable transmission line, it is known that the tap, which connects to the coaxial cable to a device can cause degradation of the signals already on the transmission line.
U.S. Pat. No. 3,559,110 discloses a coupler that allows the sampling of a signal on a coaxial cable that improves the quality of the signal output from the coupler, which signal is described as having a frequency range of between 54 to 216 megacycles. It also illustrates a manner in which AC power can be simultaneously transmitted along the coaxial cable. However, this coupler cannot be used at low frequencies and does not disclose the transmission of DC power, which is very desirable.
It is also known to use an inductor to filter out unwanted frequencies in a coupler. However, such an inductor typically needs to be manually adjusted to alter the spacing between the coil wires and fine tune the inductance in order to obtain flat attenuation characteristics over the frequency range of interest. This is cumbersome, difficult and labor intensive.
Furthermore, because the couplers and cables attached to the couplers can cause a change in the characteristic impedance of the coaxial cable transmission line, it is difficult to connect many devices to the same coaxial cable without large signal degradation.
Thus, there still exists the need for a tap that can be placed at multiple locations along a coaxial cable, still have efficient communication of RF signals over a broad range of signal frequencies and also have bidirectional capabilities for all signal frequencies.